1. Field of the Invention
The present invention, In general, relates to apparatus used as casters and, more particularly, to castering types of devices that accommodate uneven or irregular surfaces.
Casters are well known devices that assist in the mobility of a great variety of types of equipment. They are used in industry, in the home, in the medical field, and in general whenever it is desirable to move objects over a surface.
While casters function well on smooth surfaces they tend to operate less efficiently when used on uneven surfaces or surfaces which contain irregularities, or when small objects placed upon the surface are encountered by the casters. Accordingly casters have been devised which are better adapted to maneuver over uneven surfaces. However, such prior types of devices have functional characteristics which limit their suitability for certain applications.
Certain types of casters when used on uneven surfaces are inherently unstable and can cause objects supported by them to easily tip. The possibility of tipping is increased under certain circumstances, such as when changing direction or when such a type of caster is supporting and moving a load and then encounters an object on the surface which tends to restrict its forward travel.
This is because a typical caster includes a support post that is offset a distance away from the wheel axle. The load that is supported by such types of casters bears down through the support post thereby producing a tipping moment relative to the wheel axle which can, under certain conditions, make the load unstable.
Not by way of limitation but rather by way of example of an application where the above described difficulty associated with prior types of casters is realized can be found by examining the front casters of presently designed wheelchairs which tend to resist changes in direction and can at times become unstable when either direction is changed or the person sitting in the wheelchair changes his position in the chair, such as when he or she leans forward.
The reason that a change in direction is resisted by such prior types of casters is also, as was hereinabove described, attributable to an offset between the support post and wheel axle of the prior caster type. The offset is also responsible for introducing the instability that arises when the occupant leans forward.
Other certain special types of casters significantly and abruptly change their height when contacting objects on the surface. This, in turn, causes a bump which appears to abruptly change the height of the object that is supported by such a caster.
Still other prior types of casters are able to operate only one time, and must be reset after encountering an object. Still yet other prior types of casters tend to impact with objects located upon the surface, or when they encounter uneven surfaces, which in turn results in shock being transferred to the object thus supported.
Accordingly there exists today a need for a caster that is articulated to accommodate uneven surfaces and which is inherently stable.
2. Description of Prior Art
Casters are, in general, known. For example, the following patents describe various types of these devices:
U.S. Pat. No. 301,925 to Roux, Jul. 15, 1884;
U.S. Pat. No. 344,988 to Richmond, Jul. 6, 1886;
U.S. Pat. No. 1,622,447 to Kalberer, Mar. 29, 1927;
U.S. Pat. No. 1,666,139 to Johnson, Apr. 17, 1928;
U.S. Pat. No. 2,123,707 to Bloch, Jul. 12, 1938;
U.S. Pat. No. 3,433,500 to Christensen, Mar. 18, 1969;
U.S. Pat. No. 4,053,129 to Graff, Oct. 11, 1977;
and UK patent No. 4822 to Kendrick's Dec. 18, 1877.
While the structural arrangements of the above described devices, at first appearance, have similarities with the present invention, they differ in material respects. These differences, which will be described in more detail hereinafter, are essential for the effective use of the invention and which admit of the advantages that are not available with the prior devices.